1. Field of Invention
Apparatuses and methods consistent with the embodiments of present invention relate to a power transmission apparatus and an image forming apparatus having the same, and more particularly, to a power transmission apparatus for duplex printing and an image forming apparatus having the same.
2. Description of the Related Art
In general, an image forming apparatus receives image data, and forms a visual image thereof on a print medium. Image forming apparatuses have been developed that allow duplex printing function, in which both sides of the print medium are printed.
The image forming apparatus having the duplex printing function generally employs at least two or more motors since the print medium is made to pass through the developing unit once to print the first side of the print medium, and then is returned to the developing unit to pass therethrough for the second time to print the second-side of the print medium. For example, the image forming apparatus includes a developing unit driving motor for driving the developing unit, and a carrying motor that is capable of reversibly rotating to carry the print medium in the reverse direction so the same can return to the developing unit once the printing of the first side has been completed.
A conventional image forming apparatus having the duplex printing function may have to have a plurality of motors, which may contribute to the size and the production costs of the image forming apparatus.
There have been developments to use a single driving motor for both driving the developing unit and returning the print medium to the developing unit in the image forming apparatus having the duplex printing function. For example, there has been developed a structure that the driving motor drives the developing unit to rotate only in the forward direction by a unidirectional hub clutch, but which allows the print medium carrying unit to rotate in both forward and backward directions.
However, in case of the image forming apparatus 1 employing the hub clutch 30 as shown in FIG. 1, vibrations and shock may be generated in the driven gear 20 because of the repulsive force to load occurring when the driving gear 10 rotates. FIG. 2 is a graph showing an amplitude waveform according to frequency jitters of elements, which are generated while forming an image in the image forming apparatus 1 employing the hub clutch 30.
In the graph, an area A showing the peak jitter corresponds to a band around a frequency value of 65 where the frequency is generated by the hub clutch 30. Such a jitter due to the vibration and shock generated by a mating frequency between the hub clutch 30 and the driven gear 20 has an effect on the print image and may deteriorate the print quality.